Image forming apparatus and method

Abstract

An image forming apparatus includes a drum gear having a first guide slot and a cam, a clamp having a first interlocking pin inserted into the first guide slot and a cam pin is interlocked with the cam. A release lever is mounted on a support plate on which a shaft of a drum is supported. A lifter having one end with a second guide slot formed therein is coupled to the first interlocking pin. The other end of the lifter has a second interlocking pin interlocked with the release lever. The apparatus can shorten the overall printing time by reducing the additional time required for ejecting a sheet of paper because the clamp is operated in cooperation with rotation of the drum during a printing operation.

What is claimed is: 
     
       1. An image forming apparatus comprising: means for printing an image on a sheet of a print medium;   a support plate;   a rotary shaft extending from said support plate;   a drum disposed on said rotary shaft;   a drum gear disposed on said rotary shaft, said drum gear having a first guide slot formed therein and a cam surface defined thereon, said cam surface having a recessed portion;   a clamp coupled to said rotary shaft to be rotatable about said shaft and movable in radial directions of said drum, a first portion of said clamp having a first interlocking pin which is slidably received in said first guide slot and a second portion of said clamp having a cam pin with which rides along said cam surface;   a first spring coupled to said clamp to bias said cam pin towards said recessed portion of said cam surface, a clamping portion of said clamp being pressed towards said drum when said cam pin is received in said recessed portion to clamp an edge of said sheet against said drum;   s second spring;   a release lever swingably mounted on said support plate and elastically biased in a first direction by said second spring; and   a lifter rotatably coupled to said rotary shaft, one end of said lifter having a second guide slot in which said first interlocking pin of said clamp is also slidably received, and the other end of said lifter having a second interlocking pin which is engaged with said release lever when said drum is in a first position and said release lever is rotated in a second direction which is opposite to the first direction, to cause said lifter to rotate and thus cause said first interlocking pin to move relatively in said first guide slot to thereby move said cam pin along said cam surface and out of said recessed portion and thus cause said clamping portion of said clamp to move away from a surface of said drum to allow said edge of said sheet to be inserted therebetween.   
     
     
       2. An image forming apparatus as claimed in claim 1 wherein said release lever directly engages with said first interlocking pin when said drum is in a second position and said release lever is rotated in said second direction to thereby move said cam pin along said cam surface and out of said recessed portion and thus cause said clamping portion of said clamp to move away from a surface of said drum to release said edge of said sheet during a printing operation. 
     
     
       3. An image forming apparatus comprising: means for printing an image on a sheet of a printing medium;   a rotatable drum for supporting said sheet;   a cam fixed to said drum, said cam having a recessed portion;   a clamp coupled to said drum to selectively clamp the sheet to said drum, said clamp having a cam pin formed thereon, said cam pin being movable along said cam to place said clamp in a clamping position when said cam pin is received in said recessed portion and to place said clamp in a released position when said cam pin is not received in said recessed portion;   a lever cooperating with said clamp to selectively move said cam pin of said clamp out of said recessed portion;   an arm rotatably attached to said drum and having a first end and a second end, said second end being connected to said clamp;   said lever pressing said first end when said drum is in a first position, which corresponds to a sheet receiving operation, and said lever being in direct contact with said clamp when said drum is in a second position, which corresponds to a printing operation.   
     
     
       4. An image forming apparatus as claimed in claim 3, further comprising: an interlocking pin formed on said clamp;   said second end having a slot formed therein, said interlocking pin being received in said slot;   said lever being in contact with said interlocking pin when said drum is in said second position.